Hitherto, photoreceptors for electrophotography having high sensitivity to visible light have been widely used with copying machines, printers, and the like.
Gallium-aluminum-arsenic (Ga.Al.As)-based light emitting devices which are widely used as semiconductor lasers emit radiation at a wavelength of about 750 nm or more. With a view of obtaining a photoreceptor having high sensitivity to radiation of such long wavelength, various attempts have hitherto been made. For example, there has been proposed an idea that a sensitizer for effecting a wavelength increase is added to photosensitive materials, such as Se and CdS, which have high sensitivity to light of a visible ray-wave range; but this idea has a difficulty that Se or CdS has no sufficient resistance to such environmental factors as temperature and humidity. Many known organic photoconductive materials are usually limited in sensitivity to a visible-ray wave range of less than 700 nm. Indeed, few of them, if any, have good sensitivity to longer wave ranges.
Of those organic photoconductive materials, phthalocyanine compounds are known as having extended spectral photosensitivity as compared with other organic photoconductive materials. Further, in the process of .alpha.-type phthalocyanine compounds being transformed into .beta.-type phthalocyanine compounds having a stable crystal form, varieties of phthalocyanine compounds in different crystal forms have been found out. Among these photoconductive phthalocyanine compounds are, for example, X-type metal-free phthalocyanine compounds mentioned in Japanese Examined Patent Publication No. 49-4338, and .gamma.-, .gamma.', .eta.-, and .eta.'-type metal-free phthalocyanine compounds mentioned in Japanese Unexamined Patent Publications Nos. 58-182639 and 60-19151.
However, photoreceptors using these metal free phthalocyanine compounds have considerable memory effect and have not yet been found to be useful for practical application. As a matter of fact, few photoreceptors having sufficient sensitivity to long wavelength light and semiconductor laser beam and well qualified for practical use have been known, and there has been strong demand for development of such improved photosensitive material.